1. Field of the Invention
Embodiments of the present invention relate generally to a dielectric film for a semiconductor device. More particularly, embodiments of the invention relate to a high dielectric film formed by Atomic Layer Deposition (ALD), and related methods of manufacture.
A claim of priority is made to Korean Patent Application No. 10-2005-0020134, filed on Mar. 10, 2005, the disclosure of which is hereby incorporated reference in its entirety.
2. Description of Related Art
Semiconductor device manufacturers are continually striving to increase the integration density and capacity of semiconductor devices such as computer memories and other electronic data processing elements. As the integration density and capacity of the devices increases, materials with a higher dielectric constant must be used to form gate dielectric films and capacitor dielectric films in the devices. Such films formed with materials having a high dielectric constant are often referred to as “high dielectric films.”
One benefit of using high dielectric films in semiconductor devices is that they prevent leakage current that can be caused by electron tunneling. For example, where a high dielectric film is used as a dielectric for a capacitor, leakage current is prevented from passing between the capacitor's upper and lower electrodes. In general, physical thickness “t” of a high dielectric film is generally larger than the oxide equivalent thickness (Toxeq) of the high dielectric film. In other words, the high dielectric film must be thicker than a silicon dioxide (SiO2) layer with the same capacitance as the high dielectric film. For example, a SiO2 layer thinner than 20 μm generally allows significant leakage current due to electron tunneling; however a high dielectric film comprising HfO2, ZrO2, Ta2O5, or TiO2 and having the same oxide equivalent thickness (Toxeq) will have less leakage current.
Unfortunately, conventional high dielectric films used as gate insulating layers in metal-oxide semiconductor field-effect transistor (MOSFET) devices suffer from a number of shortcomings. For example, where a high dielectric film such as HfO2 or ZrO2 is used for a gate insulating layer of a MOSFET, carrier mobility in the MOSFET's channel region can be degraded by dispersion of dopants such as boron (B), phosphorus (P), and arsenic (As) from a polysilicon gate electrode above the gate insulating layer through the high dielectric film. Further, a high dielectric film comprising HfO2 can be crystallized by subsequent annealing, creating a crystallized interface with a significant amount of leakage current.
To address at least the above problems, researchers have sought ways to prevent dopant dispersion and enhance thermal stability in high dielectric films comprising an oxide layer such as HfO2. One approach that the researchers have taken is to add Al2O3 or nitrogen to the oxide to form a nitride layer or an aluminum oxide layer such as HfON or HfAlO. Although this approach is an improvement over the HfO2 layer, it is still not adequate for a transistor in a highly miniaturized device.
On the other hand, a Si-containing Hf-silicate material such as HfSiO, can be used as an alternative to HfO2. A HfSiO layer formed over a channel region of a silicon substrate generally has improved leakage current over HfO2, and it allows better charge mobility in the channel region. However, the HfSiO layer still allows the charge mobility of the channel region to be degraded by dopant dispersion from the polysilicon gate electrode above the gate insulating layer.
To further prevent the dopant dispersion and secure the thermal stability of the high dielectric film, nitrogen is often added to the high dielectric film. For example, nitrogen may be added to a high dielectric film comprising HfO2 or HfSiO to form a nitride oxide layer with a high dielectric constant. The nitride oxide layer blocks the dispersion of impurities from the polysilicon gate electrode to the channel region and improves thermal stability by raising the crystallizing temperature of the high dielectric film. When forming a nitride oxide layer such as HfON or HfSiON, nitridation may be performed by annealing an oxide layer in an environment containing NH3 . One problem with using the annealing technique to form the nitride oxide layer is that it does not allow precise control over the profile of nitrogen within the nitride oxide layer. In addition, the annealing technique must be performed as a separate process in addition to the other processes used to form the high dielectric film, thereby increasing the complexity of the methods used to form the high dielectric film.
To address the shortcomings of the conventional nitride oxide layers, new manufacturing methods have been developed, whereby a HfSiON layer is formed by ALD using an N-containing Hf precursor and a Si precursor. One of the problems with the new methods is that N-bonds may not readily form in the HfSiON layer within a thin high dielectric film. On the other hand, where N is included in a Hf precursor such as Hf[N(CH3)2]4, a N—C bond within the precursor may be so strong that carbon remains in a HfSiO layer formed by oxidizing the Hf precursor with an oxidant such as H2O. The carbon remaining in the HfSiO layer tends to degrade the electrical characteristics of the layer.
Finally, as the integration density and capacity of a semiconductor device increases, the area for each capacitor within the device decrease. Since the capacitance required for stable operation of a capacitor cannot be decreased, the dielectric constant of a dielectric film within the capacitor must be increased to provide the required capacitance. One conventional technique for increasing the dielectric constant of a dielectric film is to replace a SiO2 layer, which has a dielectric constant of about 3.9, or a Si3N4 layer, which has a dielectric constant of ˜7.2, or a composite silicon nitride/silicon oxide layer (e.g., an oxide-nitride-oxide layer), which typically has a dielectric constant of 3.9˜7.2, with a high dielectric film. However, as described above, conventional high dielectric films have numerous shortcomings.